Cassette carrier for wafer cleaning processes

ABSTRACT

An improvement of a cassette carrier is provided to improve wafer cleaning processes. The carrier includes a support and two opposed suspensions positioned at both sides of the support and each provided with a fixing mechanism for suspending edges of cassettes. According to the present invention, the structure of the carrier for carrying the cassettes is simplified to reduce amount of chemicals adhered to and remained on the surface of the carrier during wafer cleaning, thereby shortening wafer cleaning time and enhancing wafer cleaning efficiency.

FIELD OF THE INVENTION

[0001] The present invention relates generally to apparatus for wafer cleaning processes, and more particularly, to an improved cassette carrier for wafer cleaning processes.

BACKGROUND OF THE INVENTION

[0002] In the manufacture of integrated circuits (ICs), wafer cleaning technique and cleanliness considerably affect yield, quality and reliability thereof. Currently, a wet chemical cleaning technique is widely used for wafer cleaning in which wafers are sequentially rinsed in a chemical tank and a water tank, as shown in FIG. 1. In FIG. 1, a carrier 10 has a cassette 20 that is loaded with a plurality of wafers 22 to be cleaned at each side. The carrier 10 comprises a support 12 and a base 14 that has a symmetric structure to be loaded with these two cassettes 20. A cleaning tank B containing a chemical cleaning solution or de-ionized (DI) water is provided below the carrier 10. During wafer cleaning, the carrier 10 is moved by a robot A and rinsed in a plurality of cleaning tanks. The carrier 10 is rinsed in the cleaning tank B together with the cassettes 20, as shown in FIG. 2.

[0003] When wafers in the cassette 20 are moved from a chemical tank to a water tank, whether chemical remained on the wafers is removed is determined by detecting the resistivity in the water tank. According to the prior art, the chemical has been adhered to the cassettes 20 and carrier 10, which is preferably formed of a fluoride resin material such as PFA, PVDF and PTFE, and can withstand heat, chemicals and mechanical strengths. However, chemicals can be readily adhered to such material so that amount of the chemicals remained on the carrier surface is increased. Therefore, when the wafers are cleaned in the water tank, the cleaning time necessary for removing the chemicals adhered to the carrier and cassettes is increased, thereby affecting the wafer cleaning efficiency.

[0004] Consequently, it is desired to improve the wafer cleaning process in view of the above disadvantages.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to set forth an improved cassette carrier for wafer cleaning processes, in which the carrier has a decreased volume to be steeped in chemical solution so as to decrease chemicals adhered to and remained on the carrier.

[0006] According to the present invention, a cassette carrier for improving wafer cleaning processes comprises a support to be supported by a robot, and two opposed suspensions positioned at both sides of the support and provided with a fixing mechanism for suspending edges of cassettes in horizontal orientation.

[0007] One aspect of the present invention resides in that the carrier is improved to reduce the volume thereof, thereby decreasing the amount of chemicals adhered to and remained on the surface of the carrier during the wafer rinsed in a chemical tank and reducing the cleaning time in a water tank.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:

[0009]FIG. 1 and FIG. 2 are schematic views showing a conventional wafer cleaning process in a cleaning tank and equipment to be used; FIG. 3 shows a preferred embodiment of the present invention;

[0010]FIG. 4 is a schematic view showing that cassettes are carried by the apparatus shown in FIG. 3; and

[0011]FIG. 5 shows a comparison result between effects of wafer cleaning processes for the prior art carrier and the inventive carrier.

DETAILED DESCRIPTION

[0012] An embodiment of the present invention is shown in FIG. 3, in which a carrier 30 comprises a support 32 and two suspensions 34 provided at bottom of the support 32. The suspensions 34 are symmetrically positioned at both sides of the support 32. Each suspension 34 has a fixing mechanism for fixing and suspending a cassette. In this embodiment, the fixing mechanism comprises grooves 342.

[0013] The carrier 30 shown in FIG. 3 with the support 32 holding the cassettes 40 used in wafer cleaning processes is shown in FIG. 4. The cassette 40 is formed with two extended flanges 402 and an engagement part 404 at one side corresponding to the groove 342. The cassette 40 is suspended from the suspension 34 by sliding the engagement part 404 into the groove 342 and pushing the flanges 402 against the top of the suspension 34. The suspension 34 can be integrally formed with the support 32 or be coupled with the support 32 in a known manner, and it can support the cassette 40 loaded with wafers 22 and substantially maintain balance of the cassette 40.

[0014] The carrier 30 is a simplified structure which provides a robot A for fixing and supporting the cassettes 40. In this embodiment, grooves 342 are used for receiving the cassettes 40. In other embodiments, a suspension for fixing a cassette can be varied on the basis of structure of the cassette.

[0015] Apparently, compared with the prior art carrier 10, the carrier 30 according to the present invention is simplified in structure and has a reduced volume. It is advantageous in that when the carrier 30 together with the cassettes 40 and wafers 22 is cleaned in a chemical tank, amount of chemical adhered to and remained on the carrier 30 is minimized, such that time for the subsequent cleaning in a water tank can be shortened. Since the cleaning process in the chemical tank or water tank is to remove contaminant or residual chemical on the wafer, adhesion of the chemical to the carrier is undesirable. Therefore, decrease of the amount of the chemical adhered to and remained on the carrier shortens the time for the subsequent cleaning in the water tank.

[0016] As above-described, the difference of the wafer cleaning efficiencies between the carrier 10 and carrier 30 can be obtained by detecting the resistivity variation. FIG. 5 shows an experiment result in which DATA 1 shows resistivity variation when the carrier 30 is impregnated in the water tank, while DATA 2 shows resistivity variation when the prior art carrier 10 is under the same condition with water flowing at a rate of 40 LPM (Liter Per minute) and in a resistance of 8-10 MΩ before the wafer is rinsed. As known from the drawing, during wafer cleaning, when the prior art carrier 10 is impregnated in the water tank, the resistivity remarkably decreased and wouldn't rise. It is impossible for an operator to determine whether the wafers in the water tank are clean if the resistivity does not rise, since the decreased value of the resistivity might be caused by the residual chemical on the carrier 10. In the past, the cleaning operation in the water tank is finished on the basis of operator's experience and the cleaning time, and thus wafer cleaning is doubtable. If a wafer is not clean, the residual chemical will adversely affect the equipment for the subsequent spin dry process. For example, particles or rust might be caused, which would influence cleanliness of wafers. According to the carrier 30 of the present invention, the resistivity is slightly reduced and readily increased, so that the cleaning time is shortened and an operator can easily determine if the cleaning operation is completed.

[0017] In summary, the carrier of the present invention is simplified in structure, and thus the residual chemical amount during wafer cleaning is considerably decreased, thereby shortening the wafer cleaning time and improving the wafer cleaning efficiency.

[0018] While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims. 

What is claimed is:
 1. A carrier for carrying cassettes loaded with wafers in wafer cleaning processes, comprising: a support; and two opposed suspensions positioned at bottom of said support and each provided with a fixing mechanism for suspending said cassettes.
 2. A carrier according to claim 1 , wherein said fixing mechanism comprises a groove. 